OBSERVATION OF THE VISIBLE ABSORPTION-SPECTRUM OF H2O+

The A approximately 2A1 approximately - X approximately 2B1 approximately system of H2O+ has been observed, using laser absorption spectroscopy in a velocity-modulated discharge. A total of 78 transitions between 14 794 and 15 475 cm-1 have been observed with an uncertainty (1 SD) of 0.02 cm-1, including 76 transitions in the (0,7,0)-(0,0,0) band and 2 in the (0,8,0)-(0,0,0) band. This species is important for cometary astronomy, and intriguing for molecular physics because of its prominent Renner-Teller interaction. Careful measurements were made of the relative intensities of the absorption lines, which were measured to an accuracy of 13% (1 SD). This is the first observation of the A approximately - X approximately transition in absorption; all previous data were obtained in emission with conventional grating spectroscopy. The transition frequencies of our new data are in good agreement with previous work, and have improved accuracy. The new data have definite rejection of the interfering lines from excited neutral H-2 that plagued previous work. Compared with previous work, the new data have the first quantitative measurement of intensities. The ratio of the Franck-Condon factors I8/I7 = 0.99 +/- 0.43 has been measured for the first time, where I-upsilon = FCF[(0,upsilon',0)-(0,0,0)].